1. Field of the Invention
The present invention relates to a method and apparatus of sensing velocity, and, more particularly, to a method and apparatus for detecting rotational velocity and outputting a quadrature signal associated therewith.
2. Description of the Related Art
Electronic devices are an increasing part of everyday life and they are presently integrated in a large number of products, including products traditionally thought of as mechanical in nature, such as automobiles. To bridge the gap between mechanical movement and electronic control, it is necessary to successfully integrate electronic and mechanical components. This gap is normally bridged by using devices such as sensors and actuators.
Position sensors are used to electronically monitor the position or movement of a mechanical component. The position sensor produces data that may be expressed as an electrical signal that varies as the position of the mechanical component changes. Position sensors are an important part of innumerable products, providing the opportunity for intelligent control of a mechanical device.
Various contact-type sensors are known. For example, potentiometers are used, which detect a change in electrical signal due to a physical change in position of a wiping contact on an electrical resistive element. Rotational position movement can be detected by coupling a shaft of a potentiometer to the shaft of a rotating mechanical component. Linear movement can be detected either using a linear potentiometer or a rotating potentiometer that is coupled to a linear-moving component using pulleys and a string or a belt to translate a linear motion to rotational motion. A problem with this type of sensor is the physical wearing of the contacting parts. The wiping contact and the resistive element can cause a drift in the electrical signal, which induces errors and may lead to ultimate failure of the device.
Magnetic velocity sensors are generally a non-contact type of sensor and consist of a magnetic field sensing device, which is usually stationary, and a magnet is attached to a moving component. As the magnet approaches the sensing device, the magnetic field of the magnet is detected and the sensing device generates an electrical signal that is then used for counting, displaying, recording and/or control purposes. A problem with such sensors is that they depend on a movement of the magnet that is attached to a moving part, which is usually a costly approach.
A magnetic positional sensor developed by one of the inventors, patented as U.S. Pat. No. 4,970,463, and entitled “TEMPERATURE STABLE PROXIMITY SENSOR WITH SENSING OF FLUX EMANATING FROM THE LATERAL SURFACE OF A MAGNET,” discloses a Hall effect device disposed along a surface of a magnet. The magnetic field produced by the magnet is altered by the passing of a ferrous object, the alteration being detected by the Hall effect device.
A quadrature signal is generally desired to provide velocity and directional information in the form of two oscillating signals that are out of phase with each other. The phase difference between the two signals is utilized to provide directional information, i.e., a forward and reverse direction. The frequency of each of the two quadrature signals is directly proportional to the velocity of the measured component.
Current quadrature sensors generally consist of two sensors that are spaced apart a known distance in an assembly. Mechanical stack up tolerances can cause errors which effect the quality of the signal. When a single assembly is used to space the two sensors a specific distance apart to reduce tolerance problems, the assembly becomes very costly.
A problem with rotating sensors is that they often require a stationary and a movable portion within a single assembly.
Another problem is that a quadrature signal from sensors usually require two separate, spaced apart sensors.
What is needed in the art is a compact modular velocity sensor, which will provide a quadrature signal from a single module.